Untreated metal surfaces are subject to corrosion which can lead to rust development, weakening, discoloration and failure of the surface. Thus metal substrates are typically treated by a variety of methods to make the surface less reactive and more corrosion resistant. In addition, metal surfaces are often subsequently coated with decorative or additional protective coatings such as resin coatings, primers, paints and other surface treatments. Often the initial treatment of the metal surface involves a metal phosphate treatment followed by a chrome-containing rinse.
Metal objects to which surface treatments and coatings are applied can be grouped into several categories. In some industrial applications, the metal is formed into a 3-dimensional object after which any combination of surface treatments and or coating applications may be made. In a second category of industrial applications, surface treatments and or coatings are applied to the metal prior to forming when the metal is in the form of a flat sheet which is typically rolled into a coil. For many coatings applications within this category, special properties are desirable to facilitate rolling and forming operations. For coatings such as organic passivates, it may be desirable to have a high degree of hardness and block-resistance to facilitate rolling, however conventional coatings of high hardness frequently possess poor forming properties in that the integrity of the coating and ultimately its corrosion resistance is compromised by forming operations. It is desirable to provide coatings which have both high hardness and good forming properties.
It would be beneficial to develop a corrosion resistant coating composition that was inorganic and that could be used under neutral or mildly alkaline conditions. It is also important to provide a coating composition that would not prevent continued use of the other decorative surface treatments that have been used in the past. For many years coatings for metal such as organic passivate coatings have utilized hexavalent chrome stemming from its ability to inhibit corrosion. Hexavalent chrome has become less favored in the marketplace due to environmental considerations. Over time, trivalent chrome containing coatings have found greater use due to the lower level of environmental concern relative to hexavalent chrome based products. In many cases, this change has been made with a drop in corrosion resistance. It is always desirable to improve the performance properties of coatings such as corrosion resistance. This is true for any coating such as coatings based on hexavalent chrome. It would be more desirable to similarly improve performance properties such as corrosion resistance for coatings which are not based on hexavalent chrome, such as those based on trivalent chrome or non-chrome based coatings. It is also undesirable for coatings comprising chrome to leach chrome to the environment